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FOREIT REIEARCH LA
TORY
RE/ER RCH DOTE 74
MULTISPAN LOGGING OF OLD-GROWTH
TIMBER IN SOUTHWEST OREGON
DAVID H. LYSNE
STEPHEN E. ARMITAGE
ABSTRACT
Multispan
yarding systems have not been
widely used for harvesting timber in southwest Oregon. In this case study a 6-acre
stated of old-growth timber considered typical
of southwest Oregon was clearcut with a
multispan skyline system using one support
per road and a live skyline. One single-tree
and one double-tree support system were used.
Each required approximately 4 hours to rig
completely. Net production averaged 25 Mbf
per day while logging over either type of
support. The carriage passed a 7.5° deviation
from span alignment in the double-tree support
system but not a 12.25° deviation in the
single-tree system. Support-line tensions
measured in the single-tree system exceeded
predicted tensions. Support-line tensions
measured during inhaul were greatest when the
carriage was immediately uphill from the jack
and were lowest when the carriage crossed the
jack.
INTRODUCTION
In 1982 the Medford District, USDI Bureau of
Land Management (BLM) identified a 6-acre
area of old-growth timber near Azalea, Oregon
in need of a regeneration harvest. One-end
log suspension was required to protect fragile soils and ensure successful reforestation. Multispan logging was planned because
convex terrain precluded singlespan logging
and other options, including additional road
construction, were not economical.
The area was set up as a demonstration project because it was considered typical of
other possible multispan logging sites and
because multispan logging is a relatively new
concept in southwest Oregon. The timber sale
was clearcut in June 1982. We used the sale
as a case study of multispan logging and
obtained data on support-line tensions and
support rigging times. During the study, we
measured production for portions of 2 days,
Including 35 turns on two skyline roads. We
also observed logging with non-aligned skyline spans and the use of a live skyline
while logging over intermediate supports.
CHARACTERISTICS OF THE
LOGGING OPERATION
STAND CHARACTERISTICS
The
upper
ground
slopes
of
the 6-acre
demonstration area averaged 30 percent and
SEPTEMBER 1983
the
lower
slopes
60
percent.
A
complete
cruise of the demonstration area indicated it
contained an average of 40.5 merchantable
trees per acre and an average net volume of
OREGON STATE UNIVERSITY, SCHOOL OF FORESTRY
CORVALLIS, OR 97331-5704
503-753-9166
31.8 Mbf per acre. The average tree was 28
inches diameter at breast height (d.b.h.) and
contained 1.1 Mbf, gross volume. The largest
trees were 64 inches d.b.h.
anchor point was being rigged. When the final
skyline anchor point was ready, yarding was
interrupted briefly while the skyline was
moved to the final anchor point. These techniques maintained an acceptable level of pro-
ductivity and allowed an analysis of span
deviations from alignment. A single-tree sup-
LOGGING
A fan-shaped setting with two skyline roads
was used to yard logs uphill towards the
yarder on the haul road. Logs were unhooked,
decked and loaded on a lower step landing.
For each skyline road the skyline was tied to
a convenient temporary anchor point below the
single support system, the support system was
rigged and the skyline was raised and tensioned in the jack. This procedure allowed
yarding to begin
while
the
final skyline
port system and a double-tree support system
were rigged (Figs. 1 and 2). Looking downhill
from the landing, the jack in the double-tree
support system (Fig. 1) hung closer to the
right-hand support tree because the skyline
angled to the right below the jack. When the
skyline was elevated sufficiently to ensure
that a log would be partially suspended, the
horizontal
force
a
TO THIRD TAILHOLO
60
1
326.25°
-GUYLINE
TO FIRST
TAILHOLD
315.5°
TO SECOND
TAILHOLD
2 40
0
327°
-SUPPORT LINE
30
10
\ TAILHOLD
320° `
SUPPORT TREE
SUPPORT/
LINE
0
SUPPORT LINE
SUPPORT TREE
10
20
SKYLINE
Z
20
_SUPPORT TREE
10
0
324.5 °
TO SECOND
30
20
50
skyline
TO FIRST TAILHOLD
TOP VIEW
50
40
70
the
hand tree.
-GUYLINE STUMP
TOP VIEW
80
by
exerted
caused the jack to drift toward the right-
30
0
I
GUYLINE
I
PLAN VIEW n
10
20
RIGGING
GUYLINE
30
II
317 °
BLOCK
f
0
0
U'
70
PLAN VIE
30
60
20
50
-TO GUYLINE
ANCHOR
40
0
x
w
x
10
0
30
LINE
60 50 40 30 20
20
10
0
10
20 30 40 50 60 70 80
DISTANCE FROM SKYLINE (ft)
10
ANCHOR
0
80 70 60 50 40 30
r 1
20
10
10
20 30 40 50 60
FIGURE 2.
DISTANCE FROM SKYLINE (ft)
SYSTEM.
THE
DOUBLE-TREE
SUPPORT
JACK HAS BEEN ENLARGED TO SHOW
FIGURE 1.
SINGLE-TREE
SUPPORT
SYSTEM.
JACK HAS BEEN ENLARGED TO
DETAIL.
DETAIL.
THE
SHOW
OR
LOGGING EQUIPMENT
AND PERSONNEL
Specifications are
All equipment used in the demonstration was
either
shop-fabricated
or
significantly
modified, commercially available equipment.
loggers. The yarding crew was composed of a
hooktender, a rigging slinger, a choker
setter, a chaser, and a yarder operator.
given
in Table
1.
The
equipment was unique, but similar to equipment preferred by American West Coast
TABLE 1.
LOGGING EQUIPMENT SPECIFICATIONS.
Equipment)
Specifications
Yarder
(Made of spare parts assembled by logger)
Undercarriage
Tracked
Tower
46-foot-high, lattice construction
Engine
892-T Detroit diesel, approximately 430 hp
Weight
85,000 pounds fully rigged
Skyline
1,400 ft. of 1 1/4-in. wire rope2
Main line
1,400 ft. of 7/8-In. wire rope2
3,000 ft. of 5/8-in. wire rope2
1,600 ft. of 7/16-in. wire rope
H au lback
Tag line
Interlock
Drums were not interlocked
Not water-cooled
Brakes
Carriage
(Modified large model Christy)
Weight
T ruck
1,000 pounds
Not required because carriage was open-sided
Jack
(Handmade)
Weight
130 pounds, including support-line block
'AII equipment supplied by the logger, Bud Van Norman, President, Mt. Reuben Logging,
Incorporated, P.O. Box 370, Glendale, Oregon 97442.
2Additional line could have been spooled on the drums. Line lengths given are spooled
lengths used during the demonstration.
RESULTS AND DISCUSSION
USE OF A LIVE SKYLINE FOR
MULTISPAN LOGGING
was used during the yarding of this sale. The
Skyline length is usually fixed for a given
multispan setting (Binkley and Sessions 1978,
Nickerson 1980, Fodge 1981). The stretched
skyline is assumed to flow over the jack and
on the jack.
into the
located.
span
in
which
the
carriage
is
However, a live skyline, which was lengthened
or shortened within a yarding cycle as needed,
skyline always flowed easily over the jack
and through a clip used to keep the skyline
No wear was observed on the skyline after
yarding was completed. Fresh paint in the
downhill side of the jack's skyline groove
was evident after logging. However, there was
wear on the sides of the skyline groove; the
groove sides can be worn by the carriage
sheaves If skyline spans are not aligned.
3
Therefore, the wear on the downhill end of
the jack was apparently caused by deviations
from span alignment (Figs.
and 2) rather
1
than by the live skyline.
live skyline can often increase the load
capacity of multispan settings. The skyline
A
can be lengthened to increase deflection when
terrain permits, and shortened (if the yarder
has enough horsepower to retension the skyline while inhauling) when the load nears a
terrain point that limits skyline length.
Use of a live skyline reduces skyline tensions, and thus might reduce the impact that
sudden shock loadings have on the skyline and
on the yarder, both during lateral yarding
and inhauling. Use of a live skyline might
also permit easier unhooking at the landing.
DEVIATION FROM
SPAN ALIGNMENT
A deviation from span alignment is the horizontal angle created when a span deviates
from the line projected by an adjacent span.
The deviations from span alignment observed
in the demonstration project are shown in
Figures 1 and 2.
Field crews are usually advised to lay out
straight multispan settings (Kellogg 1981)
because little is known about the effects of
even slight deviations in span alignment.
Fodge (1981) identified two modes of failure
associated with non-aligned spans in doubletree support systems; neither occurred in the
demonstration project's double-tree system.
However,
a
failure due to deviations from
span alignment did occur in the demonstration
project's single-tree support system; that
failure is described at the end of this
section.
Fodge's first mode of failure is that the
support jack or the skyline can swing over
and hit a support tree when the approaching
carriage is midspan in the span below the
support. This failure
did not occur in the
demonstration project's double-tree system.
The carriage passed easily over spans with a
7.50 deviation from alignment. The skyline
chord slopes for these two spans were -42
horizontal forces pushed the support jack to
the right (Fig. 2). However, when the carriage was near the jack, the angles between
the support line and an imaginary horizontal
line on both sides of the jack became approximately equal, and the jack became nearly
centered between the support trees.
Fodge's second mode of failure is caused by a
main line rubbing against a support tree: the
rubbing can increase the risk that the support tree will buckle, or can create enough
friction to restrict lateral yarding or
gravity outhaul of the carriage. This failure
did not occur in the demonstration project's
double-tree system. The main line in the
demonstration system lay on the ground at the
terrain break; therefore, all of the main
line's horizontal force on the support tree
was directed to the base of the support tree
and did not buckle the tree. Also, the main
line
rubbed the ground near the support
tree's base, rather than rubbing the tree
itself; thus the deviation from span alignment did not cause any observable additional
restriction of lateral yarding or of gravity
outhaul. However, Fodge's second failure mode
could occur if the main line no longer lay on
the ground, but instead became sufficiently
elevated to cause the failure; this situation
could develop if long, straight slopes are
logged with intermediate supports whose spans
deviate from alignment.
The demonstration project's single-tree support system did fail in one situation caused
by
deviations
from
span
alignment.
The
failure provided detailed information about a
previously unrecognized problem associated
with deviations from span alignment.
The failure occurred in a span that deviated
12.25° from alignment and that had chord
slopes
of -39 and -46 percent. When the
carriage was a significant
distances from the jack, the jack slanted and
bisected the vertical and horizontal aspects
of the skyline chords. The skyline remained
seated in the jack. However, as the carriage
approaching
came closer to the jack, the weight of the
carriage and logs forced the jack back to a
vertical position, the skyline fell off the
jack's downhill arm and the carriage stopped.
percent and -71 percent. When the skyline was
unloaded, or was loaded and the carriage was
A jack with a deeper skyline groove might
of a span) from the support, the skyline's
1D1stance at which bisection occurred varied with each turn
and depended on log weights, skyline pretension and other
factors.
located a significant distance (more than 1/4
have retained the skyline.
4
SUPPORT-LINE TENSIONS
Accurate predictions of support-line tensions
are required for support system design. We
measured support-line tensions in the singletree support system for turns of known weight
(Table 2) to compare predicted tensions with
measured tensions. The data were collected
from the single-tree support system that had
a deviation from span alignment of 0.75° and
chord slopes of -39 and -59 percent. The data
are a subsample of tensions measured during 4
days and represent turns for which log
weights were measured and total turn weight
calculated. Total turn weights are not correlated with support-line tensions because the
skyline length varied with each turn.
peaked as a loaded carriage crossed the jack
slowly, a situation that simulated a static
analysis. Our study was based on actual
operations rather than on a simulation of a
static analysis, and produced much higher
carriage speeds than did the Peters-Aulerich
study. The highest carriage speeds encoun-
tered in our study caused the support-line
tension to peak after the carriage crossed
the jack.
TABLE 2.
SINGLE-TREE SUPPORT-LINE TENSIONS.
Totals
As the loaded carriage came from the tailhold
uphill toward the jack, the support-line
tension increased slowly until the carriage
was a few feet downhill from the jack. At
that carriage location the skyline became
very steep between the carriage and the jack,
the carriage speed decreased and the supportline tension increased to a high point (Table
column 2). The carriage thereafter suddenly ascended the skyline and appeared to
hop across the jack. Because the carriage
crossed the jack very rapidly after accelerating upward, relatively little turn weight
transferred to the jack and the support-line
2,
turn weight
(kips)
Line Tensions at Carriage
Locations (kips)
Downhill
Crossing Uphill
from
jack
the
jack
from
jack
10.1
14.3
8.7
13.1
--
16.1
6.1
5.3
5.0
13.5
13.3
-9.7
13.7
13.7
6.9
6.8
13.3
15.5
8.5
13.5
17.3
--
Avg. 6:7
13.8
9.0
llncludes carriage, jack and logs.
13.8
14.7
tension
decreased accordingly (Table 2,
column 3). As soon as the carriage was uphill
from the jack, the skyline slack from the
lower span flowed rapidly over the jack from
the lower span to the upper span, the upper
span sagged and the carriage dropped into the
sag. When all of the skyline slack from the
lower span transferred to the upper span, the
skyline tightened, catching the falling
carriage, and the support-line tension surged
to its highest point (Table 2, column 4).
Our measurements produced some unexpected
results. Not only did the maximum tension
occur at an unexpected location, but the tension was greater than we expected. A static
analysis of support-line tension predicts
that the highest tension will occur as the
carriage
crosses
the
jack
(Fodge
1981).
Peters and Aulerich,2 using a recording tensiometer, found that support-line tension
2Peters, P.A., and D.E. Aulerich. 1977. Timber harvesting
using an intermediate
sented
at
the
support system. Unpublished paper premeeting,
American
Society
of
winter
Agricultural Engineers, Chicago, Illinois, December.
We were interested in comparing predicted
support-tensions with measured tensions using
information commonly available to timber sale
planners. We predicted support-line tensions
by using equations of static equilibrium;
measurements of support-line angles; carriage, jack and average turn weights, and
measurements of the vertical force which the
skyline pretension exerts on the jack in twoand three-dimensional analyses. The constant
skyline pretension used in the calculations
was obtained from a standard multispan payload analysis (Nickerson 1980) that estimated
the standing skyline pretension required to
obtain the minimum design carriage clearance
for the turn of average weight. The two-
dimensional analysis yielded an average predicted support-line tension of 10.8 kips and
the three-dimensional analysis yielded a predicted tension of 12.9 kips. A computer
program that estimates jack loading for
various carriage positions (Nickerson 1980)
estimates the average support-line tensions
at 11.0 kips in a two-dimensional analysis
5
alternately serviced the yarder and
operated the yarder to manipulate the straw
and 13.2 kips in a three-dimensional analy-
for
dures for predicting support-line tensions,
line and haulback line used in rigging. The
demonstration project rigging time indicates
that a hooktender and a choker setter using
sis. The procedures we used, common proceoverestimated the tensions measured when the
carriage crossed the jack and underestimated
the tensions measured when the carriage was
near the jack.
INTERMEDIATE SUPPORT
RIDGING TIME
LOGGING PRODUCTION
Each support system required 4 hours to rig,
including raising the skyline. This was the
first time that the logger who participated
in
this
demonstration
project
had
a power or hand-operated winch could
rig similar supports in 3 hours, a reasonable
amount of time for the size of lines used.
either
used
standing trees to rig supports. On one previous occasion the logger hung his jack from
a line that was perpendicular to the skyline
and anchored to opposing ridgelines, a system
described briefly by Pearce and Stenzel
(1972).
The rigging crew for the demonstration project consisted of the hooktender, rigging
slinger, and choker setter. The yarder opera-
The 191 Mbf of merchantable timber (the
volume determined by the pre-sale cruise) was
logged in 15 days, for an average production
of 12.7 Mbf per day. The 15 days included
time spent on equipment rigging and dismantling, which delayed production and --
because timber sale volume was low -- had an
exaggerated effect on the production average.
The logger estimated his net production while
logging at 25 Mbf per day, based on scaled
truck loads. A subsample of 35 turns from
skyline settings taken over a 2-day
period, excluding scheduled delays, yielded a
net production of 5.5 Mbf per hour.
both
SUMMARY
Multispan logging with a live skyline and
one-end log suspension was used successfully
to log old-growth timber in a area where
convex terrain precluded the use of single
span systems and where roading was not
economical.
No problems were encountered in yarding over
a 7.5° deviation from span alignment, but the
carriage
failed
to
pass
a
12.25°
deviation
from span alignment.
Measured support-line tensions exceeded pre-
dicted tensions for carriage locations immediately uphill from the jack during loaded
inhaul and were less than predicted tensions
as the carriage crossed the jack.
CONVERSION TABLE
1 acre = 0.4047 hectare
1 foot (ft.) = 0.3048 meter (m)
1
inch (in.) =
2.54 centimeters (cm)
1 pound = 0.4536 kilogram
horsepower (hp) = 745.7 watt (W)
1
1
kip = 4.448 kiloNewton
6
LITERATURE CITED
BINKLEY, V.W., and J. SESSIONS. 1978.
Chain and board handbook for skyline
tension
Service,
and
deflection.
National Forest
USDA
System,
Forest
Pacific
Northwest Region, Portland, Oregon. 193 p.
FODGE, F.W. 1981. Engineering analysis of
forces created in two tree intermediate supports during multispan logging. Master of
Forestry Paper, School of Forestry, Oregon
State University, Corvallis, 70 p.
Research Laboratory, Oregon State University,
Corvallis. Research Bulletin 36. 15 p.
D.B. 1980. Skyline payload
analysis using a desktop computer. USDA
Forest Service, National Forest System,
Division
of
Region,
Northwest
Pacific
Oregon.
Portland,
Management,
Timber
RG-TM-012-1980. 136 p.
NICKERSON,
PEARCE,
J.K.,
and
G.
STENZEL.
1972.
KELLOGG, L.D. 1981. Machines and techniques
for skyline yarding of small wood. Forest
P. 280 in: Logging and pulpwood production.
The Ronald Press Company, New York.
The Authors
Acknowledgements
David Lysne is an assistant professor in the
Department of Forest Engineering, School of
Forestry, Oregon State University; at the
time of this study, he was Harvesting
Specialist for the Southwest Oregon Forestry
Intensified Research Program (FIR). Stephen
Armitage is the Forest Manager for the Butte
Falls Resource Area, Medford District, Bureau
of Land Management; at the time of this
study, he was Area Engineer for the Glendale
Resource Area, Medford District, BLM.
The authors wish to thank Mr. Bud Van
Norman, President of Mt. Reuben Logging,
Disclaimer
The mention of trade names or commercial pro-
ducts in this publication does not constitute
Incorporated, whose enthusiasm for new
logging techniques made this multispan timber
sale a success.
FIR is a cooperative research and technology
State
Oregon
among
effort
transfer
Land
of
Bureau
USDI
University, the
Management, USDA Forest Service, and southwest Oregon counties and timber industries.
FIR is designed to help foresters solve
complex forest management problems in southwest Oregon. This study was conducted as a
cooperative project between FIR and the
Medford District, Bureau of Land Management.
endorsement or recommendation for use.
As an affirmative action institution that complies with Section 504 of the Rehabilitation
Act of 1973, Oregon State University supports equal educational and employment opportunity
without regard to age, sex, race, creed, national origin, handicap, marital status, or religion.
7
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SCHOOL OF FORESTRY
OREGON STATE UNIVERSITY
CORVALLIS, OR 87331-5704
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us. Pa5leoe
PAID
COrvalile, OR 97331
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